Fixed & Reactivated AutoFitImageClassificationTrainTest hanging by freeing old Tensor objects

[mstfbl]

AutoFitImageClassificationTrainTest is occasionally hanging, even after PR #4939 . The issue here is that Tensor objects saved in ITransformer model (now renamed as 'estimatorModel`) are not being automatically freed by C#'s Garbage Collector, as these Tensor objects are made in TensorFlow's C libraries.

Edited on 4/9/2020: This PR makes ExperimentResult and CrossValidationExperimentResult implements IDisposable to free remaining C Tensor objects in memory in a deterministic manner. This method of freeing these objects ensures the user will not face null-reference/use-after-free errors when trying to access the model, as this clean up is done after GC runs.

Edited on 4/9/2020: I confirmed that this fixes the hanging "out of memory" and/or "long running test" issues by running AutoFitImageClassificationTrainTest for 100 iterations, in addition to running all the other unit tests in this build. In all of these builds, none of the issues described occur. These builds all time-out because running 100 iterations of AutoFitImageClassificationTrainTest takes more than 1 hour.

I have also reactivated the AutoFitImageClassificationTrainTest unit test with this fix.

**Edit: **

[mstfbl]

I am now disposing of Tensor models and their C-library objects in ExperimentResult.cs and CrossValidateExperimentResult.cs, and have added manual result.Dispose commands to the AutoML test cases. I have tested this approach in my debugging PR, and saw that no out-of-memory errors occured. Here's that test build of running AutoFitImageClassificationTrainTest for 100 iterations: https://dev.azure.com/dnceng/public/_build/results?buildId=595447&view=results #Resolved

[harishsk]

        DataViewSchema modelInputSchema,

If you are not going to support modelFileInfo being null, you should throw an exception if it is null

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Refers to: src/Microsoft.ML.AutoML/Experiment/Runners/RunnerUtil.cs:22 in 087c0d5. [](commit_id = 087c0d5, deletion_comment = False)

[mstfbl]

        DataViewSchema modelInputSchema,

With the current implementation, modelFileInfo is never null as in the case where the given root directory is null, a temp file in a temp path is returned.

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In reply to: 614421392 [](ancestors = 614421392)

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Refers to: src/Microsoft.ML.AutoML/Experiment/Runners/RunnerUtil.cs:22 in 087c0d5. [](commit_id = 087c0d5, deletion_comment = False)

[harishsk]

        DataViewSchema modelInputSchema,

Yes, but that knowledge does not exist here in this function. modelFileInfo gets passed without any validation to ModelContainer. Tomorrow, someone else may make a code change without realizing that.
It is good practice to validate your function parameters. Please add either a debug assert explicitly throw if parameter is null.

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In reply to: 614783589 [](ancestors = 614783589,614421392)

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Refers to: src/Microsoft.ML.AutoML/Experiment/Runners/RunnerUtil.cs:22 in 087c0d5. [](commit_id = 087c0d5, deletion_comment = False)

[codecov]

Codecov Report

Merging #4978 into master will decrease coverage by 2.48%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4978      +/-   ##
==========================================
- Coverage   75.81%   73.32%   -2.49%     
==========================================
  Files         993     1007      +14     
  Lines      181224   188128    +6904     
  Branches    19510    20246     +736     
==========================================
+ Hits       137387   137937     +550     
- Misses      38538    44665    +6127     
- Partials     5299     5526     +227     

Flag	Coverage Δ
#Debug	73.32% <100.00%> (-2.49%)	⬇️
#production	69.07% <100.00%> (-2.64%)	⬇️
#test	87.41% <ø> (-1.52%)	⬇️

Impacted Files	Coverage Δ
...crosoft.ML.AutoML/Experiment/Runners/RunnerUtil.cs	60.00% <ø> (ø)
test/Microsoft.ML.AutoML.Tests/AutoFitTests.cs	86.77% <ø> (ø)
...oft.ML.AutoML/Experiment/Runners/CrossValRunner.cs	92.50% <100.00%> (ø)
...L.AutoML/Experiment/Runners/TrainValidateRunner.cs	97.29% <100.00%> (ø)
.../Microsoft.ML.Vision/ImageClassificationTrainer.cs	91.16% <100.00%> (-0.05%)	⬇️
...ML.Tests/Scenarios/IrisPlantClassificationTests.cs	0.00% <0.00%> (-100.00%)	⬇️
test/Microsoft.ML.AutoML.Tests/Util.cs	50.00% <0.00%> (-50.00%)	⬇️
...st/Microsoft.ML.Functional.Tests/Datasets/Adult.cs	58.82% <0.00%> (-41.18%)	⬇️
...rc/Microsoft.ML.AutoML/API/RunDetails/RunDetail.cs	77.27% <0.00%> (-18.19%)	⬇️
...enerator/CodeGenerator/CSharp/PipelineExtension.cs	67.34% <0.00%> (-16.33%)	⬇️
... and 226 more